Structured liquid compositions are found in many products including foods, for example margarines and low fat spreads, cosmetics and personal care products and detergents products, for example liquid detergent compositions and fabric conditioning compositions.
Generally, liquid compositions, which include solutions, gels and dispersions, are produced by simple mixing of the components of the composition. The active materials which may be liquid or solid are typically added to a liquid solvent, for example water in the case of aqueous compositions, and agitated and optionally heated to produce the liquid composition. Many liquid compositions are generally produced using a stirred batch mixer.
Simple mixing to produce a liquid composition conventionally involves subjecting the components to relatively low deformation rates in the mixing process whereby a mechanical shear effect is imparted to the composition. A typical process for the production of a liquid, for example a liquid detergent composition, may involve a shear deformation rate for example of the order of 10.sup.4 sec.sup.-1 being applied to the components of the composition.
Conventional liquid compositions generally contain a relatively low level of active material due to difficulties encountered in processing. Such difficulties arise as the viscosity of the mixture of the active and liquid solvent generally increases with a higher level of active which may lead to production of an inhomogeneous mass of highly viscous and shear thinning intermediate compositions. Such compositions are difficult to disperse in mixing processes and conventional apparatus as uncontrolled phase separation may occur. Moreover, the effective functioning of the mixing apparatus may be compromised or the required energy input may be prohibitively high at high viscosities.
In some processes, the active components for example oil and surfactant may be mixed initially prior to mixing with the liquid solvent and may be solid. In order to secure adequate mixing, the active mixture is typically heated to a temperature above the melting point of the active components if solid. Heat transfer in such mixtures is typically poor due to the generally high viscosity of the active mixture and thus presents further processing difficulties.
Thus, the conventional processes in which the active components are incorporated into the liquid solvent and the concentration of the actives remains constant or increases during the process exhibit several drawbacks. These problems include shear thinning effects, inefficient operation of the mixing apparatus and poor heat transfer. Consequently careful selection of active components and the levels to be incorporated is required especially if the active component comprises a solid. As a practical drawback, the flexibility in formulation may be somewhat limited due to the sensitivity of the process to variations in formulation.
EP 580,263 discloses a process for preparing a concentrated liquid aqueous solution of a salt of an alkyl ether carboxylic acid salt and optionally adding thereto an ethoxylated and optionally carboxymethylated product derived from a polyhydric alcohol The mixture may then be diluted with water. In the Examples, a homogeneous "paste" is produced which is then diluted with water to the desired concentration. On the basis of the components disclosed, it appears that the "paste" is a concentrated solution of surfactants some of which may act as a hydrotrope. It is noted that the water is incorporated by a simple mixing process and controlled addition of the water to the paste to maintain homogeneity and avoid uncontrolled phase separation does not appear to be necessary.
GB1523678 discloses a process in which oil is added to water to produce an oil in water concentrated emulsion and then diluted with water to the desired composition. The process steps are conducted over a long period (hours) and this may represent a serious disadvantage.